1. Field of the Invention
This invention relates generally to fluid expulsion devices and more particularly to improvements in bonded diaphragm type fluid expulsion devices.
2. Prior Art
In the area of expulsion devices for fluids, particularly in zero gravity environments such as experienced in space, there are many problems associated with obtaining maximum expulsion efficiency. For example, there is a problem in maintaining a separation between the pressurant gas and the expelled liquid which may be propellant. Another problem arises in attempting to expel all of the stored fluid so as to obtain maximum efficiency. The efficiency of an expulsion device is usually measured as a percentage. This percentage is calculated by obtaining the ratio of the amount of fluid expelled to the total amound of fluid stored prior to expulsion.
One of the more common methods of solving the aforementioned problems comprises providing a diaphragm between the fluid to be expelled and the pressurization medium, typically a gas. This diaphragm or bladder is interposed between the inlet for the pressurized gas (or the tank in which the pressurant gas is stored) and the outlet for the fluid to be expelled. An example of this type of application as used in a space craft is disclosed in the U.S. Pat. to Studhalter et al., U.S. Pat. No. 2,979,897 with still another expulsion device disclosed in the U.S. Pat. to Black, U.S. Pat. No. 3,197,087. The combination of a piston and bladder is disclosed in the patent to Behman et al., U.S. Pat. No. 2,970,452. Other examples are disclosed in two U.S. patents to Everett, U.S. Pat. Nos. 3,070,265 and 3,140,802.
With the typical bladder construction, however, problems arise. For example, uneven folding can wrinkle the bladder which renders the bladder more susceptible to ripping or tearing especially if the diaphragm is of the metallic construction as required for use with many highly corrosive fluids. Also, if the bladder unfolds nonuniformly, there can be a shift of the center of gravity of the fluid to be expelled which in a missile is undesirable since this will affect the direction of thrust.
In the area of ordnance, it is desirable to have weapons that give off a minimum of sound. An example is a mortar round or grenade launcher. An example of such ordnance is disclosed in the U.S. Pat. to Gregory 1,166,360. In this patent, a bladder or diaphragm is used to separate a charge and the projectile. However, the bladder is subject to uneven unfolding and side pressures on the projectile which results in binding of the projectile in the case or loss of velocity.
Heretofore, a variety of solutions to the above problems have been proposed. One of these solutions involves bonding of the expulsion diaphragm to the wall of the expulsion container, whereby displacement of the diaphragm by the pressurizing fluid is accompanied by peeling of the diaphragm away from the container wall in a manner which achieves uniform displacement of the diaphragm without wrinkling, tearing, or other damage. Various methods of bonding the diaphragm to the container wall have also been proposed. According to one of the bonding methods of which we are aware, for example, the diaphragm is preformed and then adhesively bonded to the container wall over substantially the entire diaphragm surface in contact with the wall. The Cohen U.S. Pat. No. 3,471,349 describes another bonding method involving spray coating the wall of an expulsion container with a plastic material (polytetrafluoroethylene) to form the diaphragm on and in bonded relation to the wall. The sprayed plastic coat or layer is then baked to form the finished diaphragm.